Reduction of energy consumption of vapour compression systems, such as refrigeration systems, air condition systems or heat pumps is desired. Various efforts have been made to improve the components of vapour compression systems in order to reduce the energy consumption of the individual components, and of the vapour compression systems as such.
Furthermore, the expansion valve of a vapour compression system may advantageously be operable to control the amount of refrigerant being supplied to the evaporator to utilise the available cooling or heating capacity of the vapour compression system to the greatest possible extent.
To control an opening degree of an expansion valve of a vapour compression system in response to a differential pressure across the expansion valve is sometimes desirable. Control of the opening degree of the expansion valve occurring automatically when the differential pressure changes may also be desired.
U.S. Pat. Nos. 5,038,579, 5,052,192 and 5,002,089 all disclose an expansion valve comprising an elongated member extending into a metering port, the elongated member and the metering port cooperating to define a flow metering passage between the elongated member and the metering port. The elongated member is configured to vary the cross-sectional area of the flow metering passage in relation to the position of the elongated member to the flow metering port. Means are provided within the flow passage for controlling the position of the elongated member within the passage in response to the differential pressure across the expansion valve. The variations in the cross-sectional area of the flow metering passage defined by the elongated member are provided so that the cross-sectional area of the flow metering passage decreases smoothly and continuously as the differential pressure across the expansion valve increases.
WO 2012/072076 discloses an expansion valve for a vapour compression system, the expansion valve comprising a first valve member and a second valve member, one of the valve members being automatically movable in response to changes in a differential pressure across the expansion valve. The relative position of the first valve member and the second valve member determines an opening degree of the expansion valve. The opening degree of the expansion valve changes smoothly in response to changes in the differential pressure.
FR 2 661 977 discloses an expansion device comprising a movable piston comprising a metering port. The piston is movable inside a housing relative to an elongated member which is fixed relative to the housing, and which has a conical shape. Thereby the metering port and the elongated member cooperate to define a metering passage. A seal is required between the movable piston and the inner wall of the housing in order to provide a tight valve. This has the consequence that a certain minimum force must be applied to initiate movements of the piston, in order to overcome the friction force between the piston and the wall of the housing. Thereby it is difficult to move the piston in a precise manner, and it is not possible to adjust the flow through the valve in a precise manner. Due to the conical shape of the elongated member, the size of the metering passage changes smoothly when the elongated member moves inside the metering port. This has the consequence that the flow characteristics of the valve changes even at small changes in the position of the elongated member, and the precision of the valve is very sensitive with respect to tolerances, such as manufacturing tolerances and tolerances in the positioning of the elongated member.
U.S. Pat. No. 4,341,090 discloses a combination variable orifice valve means and check valve means to control flow between an indoor coil and an outdoor coil. The valve comprises an orifice in a valve body, and a spring-biased valve plug movable relative to the orifice and cooperating with the orifice to vary the effective area of the orifice to control the flow of fluid through the orifice. The effective area decreases smoothly and continuously as the differential pressure increases.